Solar tracking systems capable of accurately repositioning solar-energy collection devices are needed to maintain the collection devices at the proper orientation relative to the incident solar radiation. Sunlight reflectors called heliostats have long been used to maintain a beam of sunlight on a constant direction. The reflectors were rotated by clockwork or an auxiliary power supply such as an electric motor. Sunlight was used to trigger regulatory devices for the external power supply. Aside from additional energy use, electrically powered aiming systems require a power supply with a constant frequency and voltage and a separate feedback path to correct for error. Additionally, direct mechanical drives, such as worm gear actuators, are required to handle high wind loads found in an outdoor environment.
In many cases, it is desirable to use solar energy to rotate the reflector or other device (termed generally herein the collector) in the proper direction. Consequently, a number of devices have been developed which employ solar energy to direct and rotate the collector. For example, U.S. Pat. No. 4,027,651 by Robbins discloses a tracker having an arrangement of mirrors which reflect the sun's radiant energy to differentially head fluid-containing reservoirs to create a differential pressure which is used to rotate the tracker and the collector. Another tracker, disclosed by Farber et al in a "Self-Contained Solar Powered Tracking Device," ASME paper 76-WA/HT-'76, uses two sensor elements disposed on each end of a parabolic concentrator and fluidically connected to two power cylinders opposing each other through a rack and pinion gear arrangement. Unequal shading of the sensor elements causes a pressure differential which drives the power cylinders to rotate the concentrator to the desired orientation.
These devices, while effectual, are generally limited in accuracy, responsiveness, or in the type of environment in which they may be used.